1. Field of the Invention
This invention relates generally to evaporative cooling devices having wettable air permeable pads and, more particularly, to an evaporative cooling system which provides for intermittent wetting of the cooling pads and drainage of the sump pan at selected intervals.
2. Prior Art
It is well known to employ evaporative coolers to produce and direct cool air into an enclosure such as a residence. Such coolers are extremely popular, especially in arid or semi-arid regions, due in part to the fact that they require substantially less energy than compressor operated refrigeration units. Furthermore, they provide for periodic air exchange within the enclosure and for the introduction of moisture into overly dry air. They are inexpensive to purchase and comparatively simple and economical to install and maintain.
Traditionally, evaporative coolers include a box like housing which serves as the main frame. Angular corners, extending between the top and the bottom, define upright open sides, and a pad assembly, typically including a louvered frame holding a water wettable, air permeable pad, spans the opening of each side. The pads are fabricated from a saturable material such as aspen fiber.
A bottom, having an upturned peripheral edge upon which the pad assemblies rest, functions as a reservoir or sump pan for retaining the coolant liquid, usually water. A pump transfers the liquid from the reservoir to a distribution system for delivery to the pads.
Located within the housing is a blower which draws a stream of air through each of the several pads and discharges the air through a common duct communicating with the enclosure to be cooled. As the air moves through the pads, water is evaporated to absorb a portion of the heat within the air. The moisture content of the air is also raised. A float senses the water level within the reservoir and controls an inlet valve to compensate for loses due to evaporation.
Testing has shown that all other things being equal, intermittent wetting of the cooler pads produces an overall exit temperature that is lower than that achieved by conventional pad wetting methods. Such an intermittent wetting technique is described in U.S. Pat. No. 4,379,712, entitled "Evaporative Cooler", issued Apr. 12, 1983.
A significant problem associated with conventional evaporative coolers is the requirement for relatively high routine maintenance. This is due to the fact that dirt, air born contaminants and calcium build ups are washed from the pads and collect in the sump pan of the cooler. Over a period of time, these contaminants accumulate on the interior surfaces of the cooler and are recirculated through the pads degrading performance and producing a non-hygenic environment.